Pressure sensors are utilized in a wide range of sensing applications. For such applications, differential, gauge and absolute pressure sensors may accurately sense the pressure of a liquid or gaseous media. Each of these pressure sensors can be configured utilizing semiconductor technology. One of the most common types of pressure sensors is solid-state silicon pressure sensors. Such pressure sensors may incorporate a pressure sense die to exhibit a high degree of sensing accuracy. The pressure sense die provides an electrical output in response to an applied stress or pressure. The pressure sensors also can include one or two pressure ports, through which the media passes.
Some pressure sensors utilize a conductive elastomeric seal for electrically connecting a number of electrical terminals or molded-in leads to the pressure sense die. The pressure sense die can be sandwiched and compressed between an elastomeric media seal and conductive elastomeric seals contained within a plastic housing without significantly changing the output of the pressure sense die due to applied stress. These conductive seals may include two parallel, laminated conductor and insulator strips, which run from one side to the other side. Such a pressure sensor design allows the conductive seal to be slightly offset relative to the pressure sense die in the plastic housing due to manufacturing tolerances. The conductive seals can be compressed against the sense die in order to construct a pneumatic seal and effective electrical connection over the operating pressure and temperature range of the pressure sensor.
The elastomeric seals are conductive in certain precisely-determined regions so as to connect signals from the pressure sense die to the electrical terminals, which exit the housing of the pressure sensor. The conductive seals may, however, cause an electrical short if the conductor or insulator bands are forced over the edge of the pressure sense die, because the pressure sense die typically constitutes a semiconductor. In particular, electrical shorting occurs when the conductive seals wrap over the edge of the pressure sense die. The electrical shorting may short out a Wheatstone bridge or other electronic circuitry located on the sensor package such that it changes the sensor output intermittently. This intermittent sense output is difficult to detect during manufacturing and results in “die-edge shorting” in the pressure sensors.
In the majority of prior art pressure sensors, the elastomeric seals exhibit an inherent electrical shorting problem with the pressure sense die if perfect alignment is not held when the package is snapped together and the seals are compressed. The conductive seals may wrap over the edge of the pressure sense die, since the pressure sense die is slightly smaller than the package housing in order to fit the pressure sense die into the housing due to manufacturing tolerances. Therefore, die-edge shorting may occur when the pressure sense die is compressed against the seals, which can lead to a sensor malfunction or failure. Hence, it is desirable to prevent the sensing die, circuitry and electrical connections from exposure to die-edge shorting in order to ensure reliable operation of the pressure sensor.
Moreover, some current seal designs are constructed by bonding together a series of laminations of conductors and insulators utilizing adhesives, in addition to the use of a punching operation to form the hole and a slicing operation to construct individual parts. These operations can result in poorly formed parts and components that occasionally fail to meet dimensional specifications. Therefore, the pressure sensors should be constructed in such a manner that it enables the sensor parts to meet proper dimensional specifications.
A need, therefore, exists for an improved conductive seal, which achieves the elimination of die-edge shorting and which is ultimately more efficient and sturdier than presently implemented pressure sensors. Such conductive seals are described in greater detail herein.